EARTHQUAKE MAGNITUDE, INTENSITY, ENERGY, POWER LAW RELATIONS AND SOURCE MECHANISM Walter D. Mooney U.S. Geological Survey California, USA e-mail: mooney.

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Presentation transcript:

EARTHQUAKE MAGNITUDE, INTENSITY, ENERGY, POWER LAW RELATIONS AND SOURCE MECHANISM Walter D. Mooney U.S. Geological Survey California, USA usgs.gov

EARTHQUAKE CLASSIFICATION MAGNITUDECLASSIFICATION M ≥ 8.0 Great Earthquake 7.0 ≥ M < 8.0 Major / Large Earthquake 5.0 ≥ M < 7.0 Moderate Earthquake 3.0 ≥ M < 5.0 Small Earthquake 1.0 ≥ M < 3.0 Microearthquake M < 1.0 Ultra Microearthquake Hagiwara, 1964

NATURE OF EARTHQUAKES 1)Foreshocks 2)Main shock 3)Aftershocks 4)Earthquake Swarm 5)Normal Seismic activity

CLASSIFICATIONDISTANCE 1) Teleseismic Earthquake> 1000 km 2) Regional Earthquake> 500 km 3) Local Earthquake< 500 km TYPES OF EARTHQUAKES 1)Tectonic Earthquake 2)Volcanic Earthquake 3)Collapse Earthquake 4)Explosion Earthquake

EARTHQUAKE MAGNITUDE Richter Magnitude M L (Local Magnitude) M L = log A - log Ao (  ) Body-wave Magnitude (m b ) m b = log (A/T) - f ( ,h) Surface-wave Magnitude (M s ) M s = log AHmax - log Ao (  o) M S = log (A/T)max log  Moment Magnitude (M w ) M w = 2/3 log Mo M o =  A  u Duration Magnitude (M D ) M D = log   Macroseismic Magnitude (M ms ) M ms = 0.5Io + log h

Richter Magnitude Scale Distance S – P Magnitude Amplitude km sec M L mm

EARTHQUAKE INTENSITY  Rossi-Forel Intensity Scale (I – X)  Modified Mercalli (MM) Intensity Scale (1956 version), (I – XII)  Medvedev-Sponheuer-Karnik (MSK) Intensity Scale (1992 Version), (I – XII) Isoseismals Isoseismals are the curved lines joining the localities of same intensity.

EARTHQUAKE ENERGY log E = M L log E = m b log E = M s timesabout 32 times timesabout 5.5 times timesabout 3 times timesabout 1.4 times Magnitude Ground Motion Energy Magnitude versus ground motion and energy

POWER LAW RELATIONS Frequency- magnitude Relation Log 10 N = a – bM Aftershock Attenuation (p-value) N(t)  t -p Fractal Dimension

b - VALUE ESTIMATION b - VALUE ESTIMATION The Least-Square Fit Method: The log values of the cumulative number of earthquakes (N) are plotted against magnitude (M). The Maximum Likelihood Method : The maximum likelihood estimate of b-value is given by Aki ( 1965) : b =log 10 e/M-M 0

b = 0.77 Magnitude Log N An example showing frequency-magnitude relation in NE India b-value:

SOURCE MECHANISM (fault-plane solution) Classification of Faults  Thrust Fault  Normal Fault  Strike-slip Fault Dynamics of Faulting Elastic Rebound Theory  Single Couple  Double Couple

Normal fault RegimeThrust fault Regime Strike-slip fault Regime

Fault Dimension

Different Types of Faulting

Graben & Horst in Fault System

Dynamics of Faulting

Elastic Rebound Theory Reid, 1910

Plotting of P-wave First-motion (Equal Area Projection)

Equal Area Plot of a Plane and its Pole

P-wave first-motion plot and fault plane solution Kayal, 1984

Source mechanisms of earthquakes at spreading centre

Source mechanisms of earthquakes at the subduction zone, Indo-Burma ranges Rao & Kalpana, 2005